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Basic Principles of Ion Chromatography
Basic process of IC
The basic process of chromatography using ion exchange can be represented in 5 steps: eluent loading, sample injection, separation of sample, elution of analyte A, and elution of analyte B, shown and explained below. Elution is the process where the compound of interest is moved through the column. This happens because the eluent, the solution used as the solvent in chromatography, is constantly pumped through the column. The chemical reactions below are for an anion exchange process. (Eluent ion = , Ion A= , Ion B = )
Step 1: The eluent loaded onto the column displaces any anions bonded to the resin and saturates the resin surface with the eluent anion.
(key: Eluent ion = , Ion A= , Ion B = )
This process of the eluent ion (E-) displacing an anion (X-) bonded to the resin can be expressed by the following chemical reaction:
Resin+-X- + E- <=> Resin+-E- + X-
Step 2: A sample containing anion A and anion B are injected onto the column. This sample could contain many different ions, but for simplicity this example uses just two different ions ready to be injected onto the column.
Step 3: After the sample has been injected, the continued addition of eluent causes a flow through the column. As the sample elutes (or moves through the column), anion A and anion B adhere to the column surface differently. The sample zones move through the column as eluent gradually displaces the analytes.
Question to consider: How would you write the chemical reaction for elution process with respect to anion A and anion B. How would you write the Kf expression for the two reactions? How would you sketch the elution process at this step using a figure similar to the figure in Step 1 if the Kf for anion A() is larger than the Kf for anion B()?